This invention relates generally to motion control for multiaxes industrial manipulators. In particular, this invention relates to control of path velocity to constrain the machine axes velocities to predetermined limits.
In articulated manipulators having axes of rotary motion, control of a tool centerpoint along a linear path at a programmed velocity can produce machine axes velocities in excess of acceptable limits. It is known to control the rate of motion by the maximum rate of the limiting machine axis velocity or alternatively to specify non linear motion to maximize motion velocity. In this type of control some motions may be programmed to proceed on a linear path at a programmed velocity while others are programmed to proceed off a linear path at a rate determined by the greatest permitted axis velocity, the choice being left to the programmer. This programming choice adds to the complexity of creation of the overall program defining the manipulator cycle of operation and increases the risk that actual manipulator performance will differ from that desired in automatic mode.
While most instances of excess axis velocity may be readily predicted from past performance of the axis velocities within a region of any interpolated location, some manipulator structures are such that conditions are created which instantaneously require large angular changes to achieve the next desired position and orientation along a path. For example, a manipulator wrist design as is described in U.S. Pat. No. 4,068,536, must reorient two axes by 90.degree. in order for the tool to follow a path requiring a rotation perpendicular to the plane separating the inner and outer wrist segments. When such a condition occurs the velocity of the changing axes can reach excessive values virtually instantaneously. To prevent the drive motors for the wrist segments from being subjected to such excessive velocity demands, it is desired to predict when such conditions are likely to arise and constrain the path velocity as required to maintain the motor velocities within acceptable limits.
It is, therefore, one object of the present invention to provide a method and apparatus for control of linear motion of an industrial manipulator having axes of rotary motion to dynamically reduce path velocity to constrain machine axis velocities below their respective limits.
It is a further object of the present invention to provide a method and apparatus for control of motion of an industrial manipulator using current path velocity information to predict future machine axis velocities and to reduce the path velocity in response to detecting a future axis velocity in excess of its associated limit.
It is a further object of the present invention to provide a method and apparatus for control of motion of an industrial manipulator using current arm configuration and path velocity information to produce machine axis velocity signals representing future values of machine axis velocities and to reduce the path velocity in response to detecting a future axis velocity in excess of its limit.
Further objects and advantages of the present invention shall become apparent from the accompanying drawings and the description thereof.